The invention relates to an acceleration pick-up for the automatic actuation of passenger safety devices in motor vehicles during emergency conditions leading up to an accident, comprising: a housing with an interior space with an elongated round and rotationally symmetric inertial body which functions as a seismic mass therein. A transmitter for transmitting signals to a receiver through a continuous longitudinal bore provided in the inertial body. The bore constitutes a signal path from the transmitter to the receiver when the inertial body is in a rest position. The inertial body has, at one end face, a supporting base by which the inertial body is supported on a bearing in the housing. The bearing also has a through bore which is aligned with the longitudinal bore of the inertial body, when the inertial body is in a normal rest position. When a preset amplitude of acceleration is exceeded, the inertial body is deflected along its supporting base so that the transmitter can no longer send a signal through the cooperating bores to the receiver. The interruption of this signal provides the acceleration pick-up.
German Offenlegungsschrift 3 540 948 shows a similar pick-up in FIG. 6. A comparable acceleration pick-up is also shown by WO 85/04627.
Moreover, an acceleration pick-up is known from German Pat. Nos. 3,313,033 and 3,402,387, in which an inertial body is held in a rest position by a permanent magnet.
Electrical switching systems having mechanical contact making are disadvantageous in that the contacts can become contaminated, can corrode, etc. during the lifetime of the system, so that it is no longer possible to guarantee the functioning of the switch in case of need.
Known systems having optoelectronic scanning are disadvantageous in that they have a quasi analogue switching behavior.
It is therefore the object of the invention to construct an acceleration pick-up such that it functions in an especially reliable fashion during its lifetime, and when subjected to an acceleration generates a quasi digital signal with a high slope rate.
This object is achieved by having an inertial body with soft magnetic properties, and with its supporting bearing constructed in the form of an permanent annular magnet, the diameter of which corresponds approximately to the diameter of a cooperating end face of the inertial body. The diameter of a portion of the supporting base bearing is smaller than the diameter of the end face, so as to define a radially opening annular slot, starting from a flat center diameter portion of the supporting base radially outward. In this construction, the center of the inertial body end face is flat, and rests on a flat bearing surface whereas, in the outer radial portions of the adjoining end face and bearing support, there is an annular gap through which the magnetic forces are felt.
It is also advantageous to have the inertial body be made from a non-magnetic material and provided with a soft magnetic lining on its end face.
It is desirable to have a flat control portion on the end face of the inertial body, which flares upward as it radiates from the center portion to define an annular gap. Alternatively, the inertial body could have a flat surface, and its supporting member could have a flat center portion and radial downwardly flaring portions extending from the center portion to define the annular gap.
An impact absorber can be provided on the inertial body itself, or on the housing, to both prevent rebounding of the inertial element and to limit the tilting of the inertial element.
The housing can be made of a non-metallic elastic material such as rubber or plastic.
The transmitter and the receiver can be located at the same side of the housing with the transmitter sending a signal along a bore in the inertial element which is reflected back to the receiver by a reflecting element at the other end of the housing. Alternatively, the reflecting element can be omitted when the receiver and transmitter are located at opposite ends of the housing.
Good results are obtained when the angle of the aperture gap is inversely proportional to the length of the inertial body and wherein the ratio of the diameter of the flat supporting base of the inertial body to the total diameter of the body is approximately 1:1.5 to 1:5.
Various shapes of the inertial body can be utilized such as a frustum, a double frustum, a barrel, etc. For centering purposes, a trough-shaped recess can be provided in the end face of the inertia element which cooperates with a cooperating projection in the support for the inertial member.
The electronics for the output pick-up can be provided by a circuit board plugged into, or attached to one end of the housing, or located internally thereof. The output could be directed to a power supply mechanism of the safety device actuator.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.